1. Field of the Invention
The present invention relates to an inclining and rotating table apparatus for making a table surface of a rotating table incline by rotating a rotating table device having the rotating table rotatably supported by a support base.
2. Description of the Related Art
As an inclining and rotating table apparatus for making a table surface of a rotating table incline by rotating a rotating table device, there is known, for example, an inclined indexing round table which is attached on a work table of a machine tool such as a machining center (for example, refer to page 4 and FIG. 1 of Japanese Patent Application Laid-open Publication No. 2001-269829). With this inclined indexing round table, two oscillating shafts which are made to project horizontally from the support base of the rotating table device are supported respectively to two opposing columns which are provided on the main body side, in such a manner that the oscillating shafts are able to oscillate. A worm wheel is fitted to each oscillating shaft. By controlling a servomotor attached to a worm which engages with the worm wheel, each oscillating shaft is made to rotate in order to make the rotating table device incline, thereby indexing an inclined position of the rotating table.
Recently with the development of high performance electronic devices, their various parts have become smaller and higher in density, and machine tools or the like that process these various parts are also required to have high precision. Thus, it has become difficult to comply with such requirements with the precision that can be realized by conventional tools. Particularly, with a device used for continuous processing of extremely complicated curved surfaces for an inclining and rotating table apparatus, for example, even a slight eccentricity or play in the rotating table holding the workpiece, as well as in a mechanism for making the rotating table incline, will cause somewhat of a processing error in the processed components. Therefore, with the inclining and rotating table apparatus which is required an especially high process precision, there is a problem that, in addition to precision at which the rotating table is indexed, the mechanism that makes the rotating table incline also has to be ensured a high indexing precision.
Bearing structures could be major factors that render a rotating table and a mechanism for making the rotating table incline unable to ensure adequate degree of precision. Some of the reasons why a bearing that has been once assembled causes decrease in precision later on will be explained, taking a general roller bearing as an example.
1: In some cases, a gap (d) exists between the outer surface of an output shaft (a) and an inner surface of an inner race (c) of a bearing (b) with which the outer peripheral surface of the output shaft (a) contacts. As illustrated in FIG. 12, although the outer surface of the output shaft (a) and also the inner surface of the inner race (c) of the bearing (b) may be both fabricated to a perfectly round shape, if the finished measurement of the bearing (b) is too large, the gap (d) will be formed at the time the bearing is assembled. Due to this gap (d), the rotation centerline (e) of the output shaft (a), which rotates with the motion obtained by the cam mechanism, is misaligned with the rotation centerline (f) of the bearing (b). Thus, not only is high operational precision unobtainable, but also the position of gap (d) changes due to the shift in weight, thus causing abrasion between the output shaft (a) and the inner race (c) and resulting in a shortened life of the device.
2: In some cases, the outer surface of the output shaft (a) does not have a perfectly round shape. In order to prevent the problem described in the above 1, generally, interference fit is used. As shown in FIG. 13, however, if the outer surface of the output shaft (a) is not a round shape and has even a slight recess or a protrusion, then even if the inner race (c) of the bearing (b) is shaped with a satisfactory precision, when the inner race (c) is assembled to the output shaft (a), the recess or the protrusion similar to the outer surface of the output shaft (a) will appear on the inner race (c), thus distorting a bearing race surface (h) where the rollers (g) rotate. When the rollers rotate on the bearing race surface (h), due to the recesses and the protrusions of the bearing race surface (h), excessive pressure is applied to some portions of the bearing race surface (h), while some rollers fail to contact the race surface, thus making the rotating accuracy of the rollers unstable and the rotation center unstable. As a result, it is difficult for the device to operate with a high degree of precision. Moreover, excessive pressure applied between the rollers (g) and the race surface (h) causes excessive wear that shortens the life of the device.
3: In some cases, the inner surface of the inner race (c) of the bearing (b) may have recesses or protrusions. As shown in FIG. 14A which is a view before attaching the output shaft (a) and FIG. 14B which is a view after attaching the output shaft (a), if there are recesses and protrusions on the inner surface of the inner race (c) according to a different pattern from the pattern for the above-mentioned 2, then, even if the outer shape of the output shaft (a) is a perfect circle, the protruding sections on the inner surface of the inner race (c) will be pushed out by the output shaft (a), and, on the other side thereof, protruding sections will also be formed on the race surface (h) of the inner race (c). As a result, recesses and protrusions will appear on the race surface (h) of the inner race (c), thus causing the same problems as those in the above-mentioned 2.
4: In some cases, the end surface (i) of the bearing (b) is not at right angles to the output shaft (a). As shown in FIG. 15, usually an abutting portion (j) such as a flange is made to abut against the end surface (i) of the bearing (b) in order to fix the bearing (b). When the bearing (b) is abutted against the abutting portion (j), in cases where there are processing remainders on the abutting portion (j) or where dust and/or chippings are sandwiched between the bearing (b) and the abutting portion (j), the bearing (b) will be fixed in an inclined state with respect to the output shaft (a). The resulting decrease in operational precision is similar to the situation in above 1 and is such that the rotation center (f) of the bearing (b) is inclined with respect to the rotation center (e) of the output shaft (a), and therefore stable rotation cannot be obtained. These problems occur between the output shaft (a) and the inner race (c) of the bearing (b) assembled thereto.
Even when high precision type bearings which are thus commercially available are used, it is difficult to ensure high indexing precision of the table surface of the rotating table due to various factors. For this reason, there has been a need for a technique that enables high precision processing with respect to a workpiece held on a rotating table.